UNIT 10 INTRODUCTION TO TRANSDUCERS （单位10介绍传感器）.pdf

Introduction to UNIT 10 INTRODUCTION TO TRANSDUCERS Transducers and Sensors AND SENSORS Structure 10.1 Introduction Objectives 10.2 Active and Passive Sensors 10.3 Basic Requirements of a Sensor/Transducer 10.4 Discrete Event Sensors 10.4.1 Mechanical Limit Switches 10.4.2 Proximity Limit Sensors 10.4.3 Photoelectric Sensors 10.4.4 Fluid Flow Switch 10.5 Transducers 10.5.1 Position Transducers 10.5.2 Velocity Transducers 10.5.3 Force or Pressure Transducers 10.5.4 Temperature Transducers 10.6 Summary 10.7 Key Words 10.8 Answers to SAQs 10.1 INTRODUCTION Sensors can be broadly classified in two categories: discrete event and continuous. Discrete event, or on/off sensor, changes its state based on the occurrence of some external event. These sensors typically only give knowledge of two states based on the condition being sensed. They are based on mechanical, electrical or optical technology. Continuous sensors provide information over the continuous range of operation of the process and are commonly used in continuous control applications, where the process is being regulated based on continuously sensed attribute data. They are based on electrical, optical and acoustical technologies. Objectives After studying this unit, you should be able to  describe different type of sensors and transducers, and  understand the concepts of digital to analog conversion and vice-versa. 10.2 ACTIVE AND PASSIVE SENSORS The sensors can be classified as active and passive. A passive sensor has no power